GSK3 comprises two highly related proteins (GSK3-alpha and GSK3-beta) that phosphorylate a wide variety of target proteins. This kinase is expressed consitutively active in resting cells, and phosphorylation of several substrates is inhibitory, suggesting this protein kinase may repress target protein function by phosphorylation. Major targets include Glycogen synthase, ATP citrate lysate, c-Jun, c-Myc, L-Myc and tau protein suggesting roles in the control of several different biochemical pathways.